Dot matrix printers are one method of recording information stored in or generated by a data processing system. In dot matrix printers, each character or segment of a graphical image is comprised of a matrix of dots and blanks which together define the character. On close examination, the dots are arranged in a matrix of positions that together form horizontal rows and vertical columns that are adjacent, parallel and evenly spaced. The intersections of the rows and columns determine the locations of the dots and blanks, and the dots may overlap, depending on the spacing between matrix intersections and dot diameter. Each dot or blank comprising the printed character or image segment is represented in the data processing apparatus by a binary data element with a binary 1 typically representing a dot and a binary 0 typically representing a blank. Data representing a typical character may be formed from a matrix having a vertical column height of eight dot positions and a horizontal width of five dot positions, although the number of positions in either direction may vary as desired. Although alphanumeric characters are used to describe the present invention, they are exemplary because the invention may be used for any dot matrix data, including graphics.
Dot matrix printers typically include a horizontally reciprocating print head which is used to form the characters on a web such as paper. The print head usually consists of a vertically oriented column of seven or eight print wires, each of which may be selectively extended (or fired) as the print head traverses each horizontal line (or print line) of the web. When fired, the wire impacts an inked ribbon onto the web and thereby transfers the image.
It is well-known that printers, including printers of the dot matrix type, are noisy during operation. This noise distracts workers, inhibits concentration, makes conversation difficult, and is generally undesirable. Various approaches have been tried to reduce printer noise, but none have been completely satisfactory, even though some clearly recognize that the volume of the noise generated by the printer is proportional to the number of print wires firing simultaneously. A first approach simply admits that the print head is inherently noisy and focuses on tightly enclosing the printer in an effort to contain the noise. While this has met with some success, it merely masks the symptoms without solving the underlying problem. Moreover, due to the inherent necessity of opening the enclosure to feed blank paper, remove printed paper, connect cables, etc., it is not possible to satisfactorily solve the problem using this technique.
Another approach inclines the column of print wires of the print head. For example, one print head has the eight print wires arranged along a diagonal line. However, the timing of the firing of the canted print wires in this print head is complex, and does not reduce the number of simultaneous wire fires unless the character font is also specially designed to be at a different incline than the incline of the column of wires in the print head. In other words, when printing graphics, or a non-specialized font character, the noise level will not be diminished. In a related technique, the character font is specially designed to reduce the number of dots in each vertical column or slice of the character. Although fewer dots are simultaneously printed at each print location, it quiets operation only for this unique font, it is of no avail with other fonts or graphics, and it comes at the expense of degrading character resolution and quality.
In still another technique, the print head makes two passes, printing every other column on each pass. This still does not solve the noise problem because it does not reduce the number of simultaneous wire fires at each of the individual print locations.
Accordingly, it is an object of the present invention to provide a method and apparatus for quieting the operation of a dot matrix printer.
It is a further object of the present invention to provide a method and apparatus for quieting the operation of a dot matrix printer and still print all of the data dots at substantially every print location.
It is a further object of the present invention to provide a method and apparatus for quieting the operation of a dot matrix printer by reducing the number of print wires firing simultaneously at substantially every location without reducing the total number of data dots printed.
It is a further object of the present invention to provide a method and apparatus for quieting the operation of a dot matrix printer by logically allocating the data to be printed at each location into complementary submatrices which are printed during time spaced printing operations.
It is a further object of the present invention to provide a method and apparatus for selectively operating a dot matrix printer in a quiet mode of operation.